AT APRX 0600, THE ACFT DEPD GUERRERO NEGRO, MEXICO ON AN AIR TAXI FLT TO TIJUANA, MEXICO. AT 0715, THE TIJUANA WX WAS RPRTD AS PARTIALLY OBSCURED, VIS 1 MI WITH FOG, HAZE & SMOKE, WIND CALM. DRG ARRIVAL, THE PLT WAS CLRD FOR AN ILS RWY 9 APCH & RPRTD OVER THE FINAL APCH FIX. HOWEVER, THE ACFT CRASHED AT ABOUT 0759, BFR REACHING THE MIDDLE MARKER,WHICH WAS 1/2 MI FROM THE APCH END OF RWY 9. IMPACT WAS ON A RIDGE ABOUT 110 FT BELOW THE ARPT ELEVATION & APRX 100 YDS NORTH OF THE INTERNATIONAL BORDER. THE ACFT WAS FND A SHORT TIME LATER BY U.S. BORDER PATROL PSNL. NO PREIMPACT PART FAILURE OR MALFUNCTION WAS FND. THE 0800 WX AT TIJUANA WAS IN PART: SKY PARTIALLY OBSCURED, VIS 1/10 MI WITH FOG & HAZE,WIND 210 DEG AT 4 KTS. ABT 1 MI NORTH AT BROWN FIELD, THE WX WAS IN PART: SKY PARTIALLY OBSCURED, VIS 3/4 MI WITH FOG & HAZE, WIND 280 DEG AT 4 KTS. A TOXICOLOGY CHECK OF THE PLT'S BLOOD SHOWED AN ALCOHOL LVL OF 0.07%. CALCULATIONS SHOWED THE SUN WOULD HAVE BEEN 16 DEG ABV THE HORIZON ON A MAGNETIC AZIMUTH OF 89.8 DEG.